SU1203663A1 - D.c.voltage converter - Google Patents

Abstract

The invention makes it possible to increase the reliability of a constant voltage converter by eliminating switching overloads of power transformers, reducing dynamic losses and increasing frequency stability. This is achieved by introducing into the converter a synchronization generator 17 associated with the input of the forced locking unit 23, the output of which is connected to the input of the power transistors. At the moment of switching the power transistors, the control outputs 24 and 25 of the forced lock unit appear to be energized by a pulse from the generator 17. This voltage contributes to closing the power transistors 1 and 2. In the primary winding 3 of the power transformer current flows its magnetic core accumulates energy, sufficient to maintain a constant EMF of self-induction during the switching time. 2 Il. (L o about with O5 a oo Siyig /

Description

The invention relates to electrical engineering and can be used in power supply devices for automation units, computing equipment and communication facilities in which DC voltage conversion and galvanic separation of input and output circuits are required.

FIG. 1 shows a block diagram of the device; in fig. 2 - time diagrams of stresses on its elements.

The transistor inverter (Fig. 1) contains two power transistors 1 and 2, the emitters of which are combined and connected to the common bus of the inverter, and the extreme terminals of the primary winding 3 of the output transformer 4 are connected to their collectors, the outlet from the midpoint of which is connected to the plus terminal of the source 5 DC power supply, and the minus terminal of this source is connected to the offenses by the inverter bus, the secondary winding 6 of the output transformer 4 is connected to the load 7. In addition, the device contains a positive feedback circuit 8, included 1st parallel; 1 primary winding 3 of transformer 4 and consisting of series-connected ballast resistor 9, controlled key element 10, primary winding 11, switching transformer 12, secondary windings 13 and 14 of which are connected through transitions the base-emitter of power transistors 1 and 2, the synchronizing generator 17 of rectangular pulses, a pulse transformer 18 connected to the output of the generator 17, the conclusions of the secondary winding 19 of which are connected to the control input 20 of a controlled switch element 10, and the second secondary winding 21 of the same transformer 18 are connected to the synchronization input 22 of the forced-drain unit 23, the outputs 24 and 25 of which are connected to the base-emitter junctions of the power transistors 1 and 2, respectively, the startup device 26, the output of which is connected with the base of the power transistor 1.

The inverter works as follows.

When the inverter is turned on, the supply voltage from a constant current source 5 is fed to a start-up device 26, a square pulse generator 17 and a push-pull inverter cell made on power transistors 1 and 2. The start up device 26 forms a short single voltage pulse (Fig. 2a) which is applied to the base of the power transistor 1 at time point to. The latter begins to open and the potential at its collector decreases. Let at time instant to generator 17 also generate a voltage pulse (Fig. 2b), due to which the key element 10 is in the conducting state (Fig. 2c), since its control input 20 is fed to the corresponding 5

signal from the secondary winding 19 of the transformer 18. At the same time, the signal from the winding 21 of the transformer 18 to the synchronization input 22 of the block 23 of the forced locking is such that the control voltage, any outputs 24 and 25 do not affect to work the power transistor switches 1 and 2.

At the moment in time, the potential at the collector of the power transistor 1 starts

О to decrease, and the controlled key element 10 is open, but the circuits are n; i is the output terminal of the dc source 5, left is the half winding of the primary winding 3 of the output transformer 4, the collector junction

 the emitter of the power transistor switch 1, the common bus of the inverter, the negative terminal of the DC source 5, current begins to flow. Since the potential difference between the collectors of the power transistor switches 1 and 2,

0 circuit: the key element 10 ballast resistor 9, the primary winding 11 of the switching transformer 12, also begins to flow current. On the secondary winding 13 of the transformer 12, an emf is induced, facilitating the opening of the power transistor switch 1, and on the secondary winding 4, an electromotive voltage (EMF) facilitating locking of the transistor 2. Opened emf more than the power transistor switch 1.

Q The process of opening the transistor develops as an avalanche due to the presence of a positive feedback loop 8 (Fig. 2d, at time t). In the secondary winding 6 of the transformer 4, an emf is induced, due to which the energy of the source 5 of the direct current is transmitted to the load 7 (fig. 2e), the time interval to-ti). The process of transfer of energy to the load 7 occurs until the generator 17 forms a blocking voltage pulse for the key element 10 on the secondary winding

19 of the transformer 18 and the unlocking voltage pulse on the winding 20 for the forced active locking unit 23, arriving at the ei O sync input 22.

At time t, the key element 10 is closed (Fig. 2c), thereby breaking the day 8 of the positive feedback. The current in the primary winding 1 i of the transformer 12 decreases almost to zero. In the secondary winding 13 is induced EMF

0 self-induction, contributing to the locking of the power transistor 1, and in the secondary winding 14 - the EMF of self-induction, contributing to the opening of the power transistor switch 2. Simultaneously with this, the control outputs 24 and 25 of block 23

5 Forced active locking appears voltage applied to the base-to-emitter junction of power transistor switches 1 and 2, the polarity of which is removed5

It promotes the forced closing of the power transistors 1 and 2. The magnitude of the blocking voltage is greater than the EMF value that facilitates the opening of the power transistor 2.

The power transistor 1 is closed due to active closing, and the power transistor 2 remains in the closed state (Fig. 2 d and e, time interval ti-12). At the same time, the collector potential of the power transistor 1 is set equal to the sum of the potentials of the DC source 5 and the self-induced EMF of the primary winding 3 of the power transformer 4, and the collector potential of the DC transistor 2 is the potential difference of the DC source 5 and the specified self-induced EMF. When current flows through the primary winding 3 of the power transformer 4, energy is accumulated in its magnetic core. The stored energy in the magnetic core of the power transformer 4 should be enough to maintain a practically unchanged self-induced emf for a time ti - (2. This is the first necessary condition for the stable operation of the inverter.

The energy accumulated in the magnetic core of a power pulse transformer can be significantly increased due to an adjustable non-magnetic gap in the magnetic circuit, therefore the proposed magnetic circuit of the power pulse transformer is made with a gap that can be adjusted. Thus, a pause at zero is generated and the through-current mode of the power transistor switches 1 and 2 is eliminated.

At the moment of time (2, after the termination of the blocking pulse, the voltage of the generator 17, the key element 10 is opened, and the state of the control outputs 24 and 25 of the block 23 of the forced active locking is such that it does not affect the operation of the power transistors 1 and 2. So as between the collectors of power transistors 1 and 2 there is a potential difference approximately equal to twice the EMF value of self-induction of the primary winding 3 of the transformer 4, then along the circuit: collector of power transistor switch 1 (left half winding 3 armature 4), the primary winding 11 of the transformer 12, the ballast resistor 9, the key element 10, the collector of the power transistor 2, begins to flow current.

In the secondary windings 13 and 14 of the transformer 12, an electromotive force is induced to close the power transistor 1 and open the power transistor 2. Since the positive feedback circuit 8 is closed, the process develops like an avalanche and the power transistor 2 enters the saturation mode (Fig. 2 d, moment

time to). The power transistor 1 remains in the closed state, and the potential at its collector increases to a value equal to twice the voltage of the DC source 5 (Fig. 2 g) and along the circuit: the positive terminal of the source 5 constant current, right the semi-winding of the primary winding 3 of the transformer 4, the collector-emitter junction of the power transistor 2, the total torus inverter 0, the negative terminal of the DC source 5, current begins to flow. In the secondary winding 6 of the transformer 4, an electromotive force (Fig. 2e) is induced, the time t2-ta) and the energy of the constant current source 5 is transferred to the load 7, which continues until time point 3, when the generator 17 again forms a locking pulse for the key element 10 and opening for the forced active closing unit 23. Further, the processes of repetition 0 yute.

In order for the parameters of the switching transformer 12 not to affect the switching process of the power transistor switches 1 and 2, it is necessary that it be operated in linear mode. For this, transformer 12 is made as follows. so that during each working half-period, even with the maximum duration of this noluperiod, the induction increment in the magnetic circuit of the switching transformer 12 is much less than its saturation induction. In this case, it will always operate in the linear mode of the inverter in the linear mode. This is the second necessary condition for the normal operation of the proposed inverter.

The proposed transistor inverter, in comparison with the known one, completely eliminates switching overloads of power transistor switches, makes it possible to set the switching frequency of the inverter, independent of the variation of the parameters of the inverter elements. In addition, it provides the same duration of both half-periods, i.e., it eliminates the magnetisation of the power pulse transformer and ensures quick closing

0

five

POWER transistor switch by

active locking, which contributes to a significant reduction in dynamic losses. As a result, the reliability of the individual elements and the inverter as a whole increases.

Claims (1)

Invention Formula A constant-voltage converter containing an inverter cell with an output transformer, the primary winding of which is complete}) and a midpoint for connecting the power output, the secondary winding is connected to the output terminals, a switching transformer, the first winding of which through a controllable key element connected to one of the windings of the output transformer, and the second winding through the base resistors is connected to the inputs of the power transistors of the inverter cell, while the control input of the control key This element is connected to an additional winding of the transformer, characterized in that, in order to increase reliability by eliminating switching overloads of power transformers, reducing dynamic current to It; t I, I. jL.K: zq. loss and increase of frequency stability, a synchronization generator is introduced, the secondary winding of the transformer of which is connected to the input of the forced locking unit, the output of which is connected to the inputs of power transistors, and the additional winding is located on the transformer of the synchronizing generator, the output transformer is made with an adjustable non-magnetic gap, and the switching the transformer is designed so that the induction increment in its magnetic circuit is less than its induction.